A skin cytology sample can be obtained in a variety of ways, depending on the type of lesion present. In general, apply samples to a microscope slide and stain with Diff-Quik or a similar stain. Then scan the sample at 4X to 10X magnification for a representative area, and examine that area under 40X to 100X magnification.

To sample a pustule, rupture it with a needle, and smear the contents onto a microscope slide. Pustule contents can be obtained by making an impression smear on a slide after rupturing the pustule with a needle. If needed, a squash preparation can be used on thick samples to achieve a more diagnostic monolayer of cells.

If a moist or greasy lesion or lichenified skin is present, firmly press a microscope slide onto the surface of the lesion to make an impression smear sample. Clinically, lichenification and hyperpigmentation are suggestive of Malassezia dermatitis, but can also be seen with chronic bacterial infection.

For dry scaling or diffuse crusting lesions, using a dulled scalpel blade without mineral oil can help collect surface debris. If larger crusts are present, use the blade or microscope slide edge to raise the edge of the crust, and then obtain an impression smear of the exudate or debris under the crust.

For interdigital lesions, obtain samples via direct impression by pressing the interdigital web onto a slide, swabbing the interdigital web with a cotton-tipped swab and spreading the debris onto a slide, or by making acetate tape impression. In cases of paronychia, collect nail bed debris with a dull blade or the wooden end of a cotton-tipped swab, then smear the debris onto a microscope slide. Here the interdigital web is firmly pressed onto the microscope slide.

Acetate tape impressions can be used to sample dry, lichenified, and interdigital areas. For a tape preparation, firmly and repeatedly press a piece of clear (not frosted) acetate tape to the lesion (lichenified skin seen here).